Just an update for those of you in the same boat. I was able to integrate Perusall with free for teacher Canvas.
I had to get the "shared secret" and "consumer key" from Perusall. (they were very fast providing this once I explained what I was doing...but they did ask me to try it the new way....I explained it did not work).
Also do not follow the instructions you will see on the web - where they say just select Perusall in the Apps window - as they don't work and they assume your university has already connected both apps.
In Canvas - first go to Settings. Then Apps tab. Then View App Configurations. then click on + App (it is highlighted in blue).
In "Configuration Type" click on the dropdown and pick "By URL"
Put in a name (I used Perusall) and the consumer key and the shared secret.
Then under Config URL - put in this - https://perusall.com/downloads/lti-config.xml
That tells Canvas and Perusall to talk to each other (I think it is like a mini - script so they can communicate)! (I had to hunt around to find this....but I did and it seems to work).
You will get a pop up message - the app was added!
Go into Perusall - make sure you have your article or video assigned as an assignment - select it in the assignments tab - then click on "Copy full title for LMS". (this is the name you will paste into Canvas so Canvas can find the right article or video).
Go back to Canvas. Create an Assignment - under Assignment Name - paste in the title from Perusall (it has to be exact).
Give it the same points as the Perusall assignment.
Under Submission Type select External Tool. Click on Find. In the list select Perusall (if that is the name you gave it). You will see this appear in the link box https://app.perusall.com/lti/launch
Save it
It should work now. Fingers crossed!!!! When you click on the assignment it should open a new window with Perusall and jump to the title of the article you pasted in.
If not, you may have to delete the instance of Perusall in Apps and repeat all these steps.